Traditionally, manual photographic processing involved the use of at least four separate solutions: a developer to reduce the silver in the latent image to metallic silver, a stop bath to arrest the developer, a fixer to remove undeveloped silver halide salts, and a wash bath to remove residual fixer. The need for high speed developing has led to automatic processors which develop photographic film and paper.
A typical automatic processor comprises three tanks: a developer tank, a fixer tank, and a wash tank. To increase production speed, the stop bath is eliminated. However, this requires that the fixer solution be formulated with high buffering capacity to neutralize the alkaline developer carried over with the photographic film or paper.
After prolonged use, deposits can form on the surfaces of the various tanks and also on the mechanical roller/belt systems used to transport the photographic materials through the processor. In the developer tank, the deposits can be metallic silver, silver salts, and alkali metal salts. In the fixer tank, the deposits can be silver salts, alkali metal salts, and elemental sulfur. Finally, in the wash tank, the deposits can be alkali metal salts, gelatin, and gelatin by-products.
The prior art discloses the use of separate cleaning compositions for the developer and fixer tanks. A strong oxidizer plus a solvent for silver salts is used on the developer tank. Typically, such a cleaner includes chromic acid or chromate salts plus sulfuric or sulfamic acid. The cleaner can be formulated as a powder or liquid. In addition, a neutralizer, such as an alkali bisulfite solution, is used to remove residual chromate salts. Other variations include alkaline powders which are combinations of alkali thiosulfate and ammonium sulfate or other ammonium salts. More recently, a powdered product consisting of a peroxymonosulfate compound, sold under the name OXONE (a trademark of E. I. Dupont de Nemours Company), and citric acid has been developed.
The major problem with non-chromate based cleaners is the time involved in cleaning. The OXONE.TM./citric acid cleaner usually requires at least eight to ten hours to effectively remove all residues. Even after this time, it does not always remove the organic "tar" residues found in tanks used for processing color film and paper.
In cleaning the fixer tank, a strong caustic solution, such as sodium or potassium hydroxide, is normally employed to dissolve the silver complexes and salts. In addition, powdered products are available which typically consist of trisodium phosphate. Such caustic solutions suffer the disadvantages of being injurious to the eyes and skin. Also, phosphates are banned in many localities. The wash tanks are normally contaminated with alkali metal salts and gelatinous residue resulting from the growth of microorganisms in the tank and gelatin residue from the film or paper. Generally, chlorine bleach is used to clean and disinfect the wash tanks. However, chlorine bleach does not effectively dissolve alkaline metal salts.